High energy density batteries such as Li—S batteries are more and more in demand as the use of portable electronic devices increases. Chemical reactions in Li—S batteries are based on conversion reactions occurring with the phase changes between solid phases and soluble intermediates; whereas in conventional batteries the chemical reactions are based on intercalation reactions occurring within well-defined solid media. Cathodes in Li—S batteries thus undergo important morphological and volumetric changes. This constitutes one of the fundamental challenges when it is desired to manufacture a Li—S battery with a long life cycle. A simplified reaction scheme in a Li—S battery is as follows:

The chemical reactions at each step are as follows:S8(solid)+2Li++2e−→Li2S8(soluble); 0.25 electron/S (209 mAh/g)  (I)Li2S8(soluble)+2Li++2e-→2Li2S4(soluble); 0.25 electron/S (209 mAh/g)  (II)Li2S4(soluble)+2Li++2e−→2Li2S2(solid); 0.5 electron/S (418 mAh/g)  (III)Li2S2(solid)+2Li++2e−→2Li2S (solid); 1 electron/S (836 mAh/g)  (IV)
The solid products in the chemical reactions outlined above present a high resistivity in both electron conductivity and lithium-ion conductivity. Accordingly, control of the morphology of these solid products is an important factor in the determination of the reversibility of a Li—S battery (Jianming Zheng et al., “Controlled Nucleation and Growth Process of Li2S2/Li2S in Lithium-Sulfur Batteries”, Journal of Electrochemical Society 2013, 160(11), A1992-A1996). Various control strategies are known in the art.
One strategy developed for the morphological control of the solid products in a Li—S battery consists of confining the active sulfur inside a conductive matrix (generally a carbon-based material). Such conductive matrix may be for example mesoporous carbon (X. Ji, L. F. Nazar, J. Mat. Chem. 20 (2010) 9821-9826), carbon in hollow sphere form (N. Jayaprakash, J. Shen, S. S. Moganty, A. Corona, L. A. Archer, Angew. Chem. 123 (2011) 6026-6030), carbon nanotubes (CNTs) (G. Zheng, Q. Zhang, J. J. Cha, Y. Yang, W. Li, Z. W. Seh, Y. Cui, Nano Lett. (2013) 13, 1265-1270) or graphene layers (L. Ji, M. Rao, H. Zheng, L. Zhang, Y. Li, W. Duan, J. Guo, E. J. Cairns, Y. Zhang, J. Am. Chem. Soc. 133 (2011) 18522-18525).
The above various approaches based on confinement of sulfur inside a conductive matrix have yielded interesting results, which confirms that high energy batteries Li—S are promising. However, there are still many drawbacks associated to these batteries. Firstly, sulfur confinement is not always perfect or permanent. After a certain number of cycles, soluble sulfurs diffuse outside the matrix and into the electrolyte. Secondly, the volumetric energy density of the cell is not better than that of a conventional Li-ion battery, due to the very low density of the composite carbon. Thirdly, the confinement process is not economically viable on a large scale, which renders commercialization difficult.
Other strategies for the morphological control of the solid products in a Li—S battery are based on the nature of the electrolyte used in the cell. Such approaches are disclosed for example in U.S. Pat. Nos. 7,019,494, 7,646,171, U.S. 2006-0208701 and U.S. 2005-0156575.
Moreover, other strategies have been attempted based on the charge and/or discharge of the Li—S battery. Such processes are disclosed for example in Yu-Sheng Su et al., “A Strategic Approach to Recharging Lithium-Sulphur Batteries for Long Cycle Life”, Nature Communications, published Dec. 18, 2013; U.S. Pat. No. 8,647,769.
There is still a need to develop strategies for improving the performance and characteristics of Li—S batteries.
The present description refers to a number of documents, the content of which is herein incorporated by reference in their entirety.